1. Field of the Invention
The present invention relates generally to railtrucks for use in supporting cars for movement along parallel rails or tracks, and more particularly to a railtruck suspension for supporting such railtrucks on wheel and axle sets of known construction.
2. Discussion of the Prior Art
It is known to provide an H-shaped railtruck for use in supporting a railcar on longitudinally spaced wheel and axle sets for movement along a pair of laterally spaced rails. A particular prior art construction is illustrated in U.S. Pat. No. 5,107,773, to Daley et al., and generally includes the railtruck -frame presenting four integral corner pedestals that receive wheel bearing housings within which the axles of the wheel sets are supported for rotation. A primary suspension is provided between the frame and each bearing housing for supporting the frame on the wheel and axle sets. A tie bar extends beneath each bearing housing and is fastened to the pedestal both in front of and in back of the housing for lifting the housing with the frame when the frame is raised.
Each bearing housing in the known construction forms a complete enclosure of the bearing therein, and is installed in an outboard bearing construction by sliding it horizontally over the bearing or journal after the wheels are pressed on the axle. In an inboard bearing construction of the apparatus, the bearing housing must be installed before the wheels are pressed on the axle.
The primary suspension between the frame and each bearing housing in the noted prior art construction includes front and rear elastomeric suspension members supported between the frame and the housing, wherein each member consists of a plurality of elastomeric pieces sandwiched between thin metal plates. The pieces and plates are both of chevron shape. The suspension members support the bearing housing so that upward movement of the housing produces compression of the elastomeric portions, increasing the vertical constraint that they provide and centering the vertical travel. Thus, the primary spring suspension units provide flexibility vertically, longitudinally and transversely to give control of wheel and axle set motions to reduce shock and vibration plus minimize hunting oscillations. Damping of the vertical motion can be provided by dampers connected between the housings and the frame.
Each of the suspension members in the prior art construction are mounted on the frame by an L-shaped intermediate mounting member having a long vertical portion presenting a vertical surface that mates with a corresponding vertical surface of the associated pedestal, and a short horizontal portion presenting an upper horizontal surface that bears against a lower horizontal face of the pedestal. The long vertical portion is tapered, presenting a wedge shape in side elevation, and presents a support surface opposite the vertical surface for supporting one of the suspension members. Retainers are provided for holding the intermediate mounting members in place on the pedestals, and extend through the tie bars and the short horizontal portions of the members. If it is necessary to adjust the vertical position of a bearing housing in its pedestal, e.g. because of wheel tread wear, this can be done by placing horizontal shims of the necessary thickness between the upper surfaces of the intermediate members and the lower horizontal surfaces of the pedestal that are associated with the housing.
In order to remove an axle from the railtruck of the known construction, it is necessary to first remove the tie bars from the two pedestals supporting the axle, and to raise the frame above the primary suspension members so that the chevron suspension members and the L-shaped intermediate mounting members fall to the ground. Thereafter, if the construction is an outboard bearing type, the axle can be rolled out and one or both of the bearing housings can be removed from the axle. Reassembly of the axle follows these steps in reverse, requiring that the suspension members and the intermediate mounting members be held in place by hand until the frame is lowered, loading the suspension members. Thus, several workers must cooperate to assemble the axle on the railtruck, and a relatively long time is required to complete the operation.
Shimming for wheel wear in the known construction is also relatively complicated, requiring again that the tie bar be removed from the pedestal at which shims are to be installed. Thereafter, the frame is raised to remove the load from the primary suspension members and produce a space for the shims. However, the frame must not be lifted too far or the suspension members will fall to the ground. Once a space is provided between the horizontal surfaces of the intermediate mounting members and the pedestal, shims are inserted and the frame is lowered to load the suspension members. The tie bars are then fastened in place to complete the operation.
The noted prior art construction does not allow for shimming to compensate for machining variations. Therefore, very tight tolerances must be maintained during machining, and non-conforming results must be welded and re-machined, adding to the cost of manufacture of the railtrucks. In addition, there is no provision for shimming for settlement of the chevron suspension members or for axle tram independent of machining tram. Thus, the construction does not permit the necessary adaptability to enable long use of the component parts thereof.
During the development of an improved railtruck apparatus, the inventors were made aware of new requirements that were being considered by regulators. The Amtrak High Speed Trainset Specification 558, issued on Apr. 17, 1995, states the new requirement as being 25% maximum wheel load change at 2.25" of height change at one wheel. Railtrucks having equal or less change are in compliance.
The requirement of 25% at 2.25" would effectively eliminate many types of previously considered acceptable rail passenger trucks including the prior art construction discussed above which shows about 40% wheel load change. No known type of outboard journal rigid frame railtruck with primary suspension at the journal box would comply with the new requirements. The wider frame possible with outboard journal railtrucks is sometimes preferred because it provides more space for mounting propulsion and braking equipment, and because it results in higher roll resistance which improves the ride performance. An advantage of inboard railtrucks is that they have improved wheel load-equalization characteristics due to geometry. However, even known inboard railtruck constructions would have difficulty complying with the new requirements.
There are two known types of passenger railtrucks that would comply with the noted requirements. The first is a fully equalized rigid frame truck having an added member called an equalizer beam that transmits the load from the frame to the journal box. The primary springs in this known construction are spaced closely enough to improve the wheel load equalization. The second type of passenger railtruck in compliance with the requirements is an articulated frame railtruck, of which one design has spherical ball joints or elastomer elements installed on a somewhat diagonal centerline to join two sides of the frame set, effectively forming a hinge line. This reduces the effect of raising or lowering one wheel by removing the rigidity of the frame.